High-power white LED devices whose application to generic illumination has been studied demand encapsulation materials having light resistance and heat resistance. In recent years, so-called “addition curing type silicone” has been heavily used.
This addition curing type silicone is one obtained by thermal curing of a mixture mainly composed of a silicone derivative having a vinyl group on a main chain thereof and a silicone derivative having an SiH group on a main chain thereof in the presence of a platinum catalyst. For example, Patent Document 1 discloses a resin composition which provides a cured material having excellent transparency and insulating characteristics, obtained by introducing an organopolysiloxane into a composition to set a molar ratio of a silicon-bonded hydrogen atom in the composition and an alkenyl group to a specific range.
Patent Document 2 discloses a resin composition containing a silicone resin having at least two silicon atom-bonded alkenyl groups in one molecule thereof and an organohydrogensilane and/or an organohydrogensiloxane each having at least two silicon atom-bonded hydrogen atoms in one molecule thereof.
Patent Document 3 discloses a composition which gives a cured material with an excellent strength by using a linear polyorganohydrogensiloxane having a silicon atom-bonded hydrogen atom (an Si—H group) midway a molecular chain thereof in combination with a linear polyorganohydrogensiloxane having an Si—H group at both ends of a molecular chain thereof in specific amounts.
On the other hand, in the addition curing type silicone resin, since a platinum catalyst with high activity is generally used, when a curing reaction once starts, it is extremely difficult to stop the reaction halfway, and it is difficult to form a semi-cured state (stage B). Then, for the purpose of lowering the catalytic activity of the platinum catalyst, it is known to be effective to add a phosphorus compound, a nitrogen compound, a sulfur compound or an acetylene as a reaction inhibitor (see, for example, Patent Document 4).    Patent Document 1: JP-A-2000-198930    Patent Document 2: JP-A-2004-186168    Patent Document 3: JP-A-2008-150437    Patent Document 4: JP-A-6-118254